Process for beneficiating unground pebble phosphate ore



United States Patent 3,349,903 PROCESS FOR BENEFICIATING UNGROUND PEBBLE PHOSPHATE ORE Clarence G. Olsen, Lakeland, Fla., assignor to W. R.

Grace & C0., New York, N.Y., a corporation of Connecticut No Drawing. Filed Dec. 28, 1966, Ser. No. 605,180 10 Claims. (Cl. 2093) ABSTRACT OF THE DISCLOSURE In abstract, this invention is directed to a process for beneficiating unground pebble phosphate ore comprising: (a) mining'pebble phosphate ore matrix; (b) preparing a pulp of the unground matrix; (0) flowing the pulp to a washing plant; ((1) disintegrating mud ball-s present in the pulp; (d) desliming the pulp; (e) wet screening the pulp to obtain a first fraction of pulp, substantially all particles of which pass a 5 mesh screen and are retained on a 150 mesh screen; (f) subjecting the first fraction to froth flotation to produce phosphate-rich concentrates and phosphate-poor railings, all as described hereafter.

This application is a continuation-in-part of copen-ding application Ser. No. 400,217, filed Sept. 29, 1964, and now abandoned.

This invention is in the field of ore beneficiation, more particularly it is in the field of phosphate ore beneficiation using beneficiation steps including froth flotation.

Prior art methods of beneficiating phosphate ore using steps including froth flotation are taught by U.S. Patent Nos. 2,293,640, 2,914,173, 3,099,620, and 3,013,664. In the prior art froth flotation has not been successfully applied to phosphate ore pulps made from unground ore containing oversize particles (e.g., particles retained on a 35 mesh screen, U.S. Patent No. 2,914,173, or particles retained on a 14 mesh screen, U.S. Patent No. 3,013,664).

In the process of the instant invention, unground, deslirned pebble phosphate ore having a particle size distribution of about:

Weight percent is beneficiated by froth flotation. Thus, as will be readily apparent to those skilled in the art, the process of the instant invention constitutes a very substantial technical advance over the methods of the prior art.

In summary, thisinvention is directed to a method for beneficiating unground pebble phosphate ore comprising: (a) mining a pebble phosphate ore matrix; (b) preparing an aqueous unground pulp of said matrix; (c) flowing said aqueous pulp to a washing plant; (d) disintegrating mud balls present in said aqueous pulp without grinding said pulp; (e) desliming the washed aqueous pulp; (f) wet screening the deslirned unground aqueous pulp and 3,349,903 Patented Oct. 31, 1967 collecting a first sized fraction of the unground aqueous pulp, the solid particles of said first sized fraction having a particle size distribution of about:

U.S. Standard mesh Weight pegcent (g) preparing a first feed pulp from the first sized fraction of unground aqueous pulp by adjusting the solid content of said first sized fraction to about 20-30%; (h) preparing a first rougher feed from said first feed pulp by adjusting the pH of said first feed pulp to about 8.5-11; (i) subjecting said first rougher feed to froth flotation in at least one first rougher flotation cell in the presence of an anionic flotation reagent to produce a phosphate-rich rougher overflow concentrate and a phosphate-poor rougher underflow tailing; (j) recovering the phosphate-rich rougher overflow concentrate for further concentration in later recite-d step; (k) separately recovering the phosphate-poor rougher underflow tailing for further concentrating in later recited steps; (1) desliming the phosphate-poor rougher underflow tailing by washing said tailing with water; (In) preparing a first thick pulp by dewatering the washed and deslirned phosphatepoor rougher underflow to a solid content of about 65- (n) preparing a second feed pulp by adding fresh Water to adjust the solid content of the first thick pulp to about 20-30%; (0) preparing a scavenger feed pulp by adjusting the pH of the second feed pulp to about 6.8-7.3; (p) subjecting the scavenger feed pulp to froth flotation in at least one scavenger flotation cell in the presence of a cationic flotation reagent to produce a phosphate-rich scavenger underflow concentrate and a phosphate-poor scavenger overflow tailing; (q) recovering the phosphate-rich scavenger underflow concentrate for further concentration in later recited steps; (r) discarding the phosphate-poor scavenger overflow tailing; (s) preparing a mixed pulp by combining the phosphaterich rougher overflow concentrate and the phosphaterich scavenger underflow concentrate; (t) treating the mixed pulp with mineral acid; (u) partially dewatering and partially deoiling the acid-treated mixed pulp; (v) deoiling the partially deoiled acid-treated mixed pulp by washing said mixed pulp with water; (w) preparing a second thick pulp by dewatering the water-washed acid-treated mixed pulp to a solid content of about 65- 75%; (x) preparing a third feed pulp by adjusting the water content of the second thick pulp to about 20- 30%; (y) preparing a cleaner fee-d pulp by adjusting the pH of the third feed pulp to about 6.8-7.3; (2) subjecting the cleaner feed pulp to froth flotation in at least one cleaner flotation cell in the presence of a cationic flotation reagent to produce a phosphate-rich cleaner underflow concentrate and a phosphate-poor cleaner overflow tailing; (aa) recovering the phosphate-rich cleaner underflow concentrate; and (bb) discarding the phosphatepoor cleaner overflow tailing.

U.S. Standard mesh: Weight percent (g) preparing a first feed pulp from the first sized fraction of unground aqueous pulp by adjusting the solid content of said first sized fraction to about 20-30%; (h) preparing a first rougher feed from said first feed pulp by adjusting the pH of said first feed pulp to about 8.5-11; (i) subjecting said first rougher feed to froth flotation in at least one first rougher flotation cell in the presence of an anionic flotation reagent to produce a phosphate-rich rougher overflow concentrate and a phosphate-poor rougher underflow tailing; (j) recovering the phosphaterich rougher overflow concentrate for further concentration in later recited steps; (k) separately recovering the phosphate-poor rougher underflow tailing for further concentrating in later recited steps; (1) treating the phosphaterich rougher overflow concentrate with mineral acid; (m) partially dewatering and partially deoiling the acid-treated phosphate-rich rougher overflow concentrate; (n) deoilin g the acid-treated partially dewatered and partially deoiled phosphate-rich rougher overflow concentrate by washing said concentrate with fresh water; (0) preparing a first thick pulp by further dewatering the deoiled phosphaterich rougher underflow concentrate to a solid content of about 65-75%; (p) preparing a second feed pulp by adding fresh water to adjust the water content of the first thick pulp to about 20-30%; (q) preparing a cleaner feed pulp by adjusting the pH of the second feed pulp to about 6.8-7.3; (r) subjecting the cleaner feed pulp to froth flotation in at least one cleaner flotation cell with an anionic flotation reagent to produce a phosphate-rich cleaner underflow concentrate and a phosphate-poor cleaner overflow tailing; (s) recovering the phosphate-rich cleaner underflow concentrate; (t) separately recovering the phosphate-poor cleaner overflow tailing for further concentration in later recited steps; (u) forming a mixed pulp by combining the phosphate-poor rougher underflow tailing and the phosphate-poor cleaner overflow tailing; (v) treating the mixed pulp with mineral acid; (w) partially dewatering and partially deoiling the acid-treated mixed pulp; (x) deoiling the acid-treated partially de- Watered and partially deoiled first mixed pulp by washing said pulp with fresh water; (y) forming a second thick pulp by desliming and dewatering the deoiled mixed pulp to a solid content of about 50-60%; (2) forming a third feed pulp by adding fresh water to adjust the solid content of the second thick pulp to about 20-30%; (aa) forming a scavenger feed pulp by adjusting the pH of the third feed pulp to about 6.8-7.3; (bb) subjecting the scavenger feed to froth flotation in at least one scavenger flotation cell in the presence of a cationic flotation reagent to produce a phosphate-rich scavenger underflow concentrate and a phosphate-poor scavenger overflow tailing; (cc) recovering the phosphate-rich scavenger underflow concentrate; and (dd) discarding the phosphate-poor scavenger overflow tailing.

In other preferred embodiments, unground pebble phosphate ore is beneficiated by methods comprising:

(1) Mining a pebble phosphate ore matrix; (a) preparing an aqueous unground pulp of said matrix; (b) flowing said aqueous pulp to a washing plant; (c) disintegrating mud ball present in said aqueous pulp without grinding said pulp; (d) desliming the washed aqueous pulp; (e) wet screening the deslimed unground aqueous pulp and collecting a first sized fraction of the unground aqueous pulp, the solid particles of said first sized fraction having a particle size distribution of about:

U.S. Standard mesh: Weight percent (f) preparing a first feed pulp from the first sized fraction of unground aqueous pulp by adjusting the solid content of said first sized fraction to about 24-26%; (g) preparing a first rougher feed from said first feed pulp by adjusting the pH of said first feed pulp to about 8.5-9.5; (h) subjecting said first rougher feed to froth flotation in at least one rougher flotation cell in the presence of an anionic flotation reagent to produce a phosphate-rich rougher overflow concentrate and a phosphate-poor rougher underflow tailing; (i) recovering the phosphate-rich rougher overflow concentrate for further concentration in later recited steps; (j) separately recovering the phosphatepoor rougher underflow tailing for further concentrating in later recited steps; (k) desliming the phosphate-poor rougher underflow tailing by washing said tailing with water; (1) preparing a first thick pulp by dewatering the washed and deslimed phosphate-poor rougher underflow to a solid content of about 69-71%; (m) preparing a second feed pulp by adding fresh water to adjust the solid content of the first thick pulp to about 24-26%; (11) preparing a scavenger feed pulp by adjusting the pH of the second feed pulp to about 6.8-7.3; (o) subjecting the scavenger feed pulp to froth flotation in at least one scavenger flotation cell to produce a phosphate-rich scavenger underflow concentrate and a phosphate-poor scavenger overflow tailing; (p) recovering the phosphaterich scavenger underflow concentrate for further concentration in later recited steps; (q) discarding the phosphatepoor scavenger overflow trailing; (r) preparing a mixed pulp by combining the phosphate-rich rougher overflow concentrate and the phosphate-rich scavenger underflow concentrate; (s) treating the mixed pulp with mineral acid; (t) partially dewatering and partially deoiling the acid-treated mixed pulp; (u) deoiling the partially deoiled acid-treated mixed pulp by washing said mixed pulp with water; (v) preparing a second thick pulp by dewatering the water-washed acid-treated mixed pulp to a solid content of about 69-71%; (w) preparing a third feed pulp by adjusting the water content of the second thick pulp to about 24-26%; (x) preparing a cleaner feed pulp by adjusting the pH of the third feed pulp to about 6.8-7.3; (y) subjecting the cleaner feed pulp to froth flotation in at least one cleaner flotation cell in the presence of a cationic flotation reagent to produce a phosphate-rich cleaner underflow concentrate and a phosphate-poor cleaner overflow tailing; (z) recovering the phosphaterich cleaner underflow concentrate; and (aa) discarding the phosphate-poor cleaner overflow tailing;

(2) Mining a pebble phosphate ore matrix; (a) preparing an aqueous unground pulp of said matrix; (b) flowing said aqueous pulp to a washing plant; (c) disintegrating mud balls present in said aqueous pulp without grinding said pulp; (d) desliming the washed aqueous pulp; (e) wet screening the deslimed unground aqueous pulp and collecting a first sized fraction of the unground aqueous pulp, the solid particles of said first sized fraction having a particle size distribution of about:

U.S. Standard mesh: Weight percent (f) preparing a first feed pulp from the first sized fraction of unground aqueous pulp by adjusting the solid content of said first sized fraction to about 24-26%; (g) preparing a first rougher feed from said first feed pulp by adjusting the pH of said first feed pulp to about 8.5-9.5; (h) subjecting said first rougher feed to froth flotation in at least one first rougher flotation cell in the presence of an anionic flotation reagent to produce a phosphate-rich rougher overflow concentrate and a phosphate-poor rougher underflow trailing; (i) recovering the phosphaterieh rougher overflow concentrate for further concentration in later recited steps; (j) separately recovering the phosphate-poor rougher underflow tailing for further concentrating in later recited steps; (k) treating the phosphate-rich rougher overflow concentrate with mineral 'acid; (1) partially dewatering and partially deoiling the acid-treated phosphate-rich rougher overflow concentrate; (in) deoiling the acid-treated partially dewatered and partially deoiled phosphate-rich rougher overflow concentrate by washing said concentrate with fresh water; (11) preparing a first thick pulp by further dewatering the deoiled phosphate-rich rougher underflow concentrate to a solid content of about 69-71%; (0) preparing a second feed pulp by adding fresh water to adjust the water content of the first thick pulp to about 24-26%; (p) preparing a cleaner feed pulp by adjusting the pH of the second feed pulp to about 6.8-7.3; (q) subjecting the cleaner feed pulp to froth flotation in at least one cleaner flotation cell in the presence of a cationic flotation reagent to produce a phosphate-rich cleaner underflow concentrate and a phosphate-rich cleaner underflow concentrate and a phosphate-poor cleaner overflow tailing; (r) recovering the phosphate-rich cleaner underflow concentrate; (s) separately recovering the phosphate-poor cleaner overflow tailing for further concentration in later recited steps; (t) forming a mixed pulp by combining the phosphate-poor rougher underflow tailing and the phosphatepoor cleaner overflow tailing; (u) treating the mixed pulp with mineral acid; (v) partially dewatering and partially deoiling the acid-treated mixed pulp; (W) deoiling the acid-treated partially dewatered and partially deoiled first mixed pulp by washing said pulp with fresh water; (x) forming a second thick pulp by desliming and dewatering the deoiled mixed pulp to a solid content of about 55-58; (y) forming a third feed pulp by adding fresh water to adjust the solid content of the second thick pulp to about 24-26%; (2) forming a scavenger feed pulp by adjusting the pH of the third feed pulp to about 6.8-7.3; (aa) subjecting the scavenger feed to froth flotation in at least one scavenger flotation cell in the presence of a cationic flotation reagent to produce a phosphate-rich scavenger underflow concentrate and a phosphate-poor scavenger overflow tailing; (bb) recovering the phosphate-rich scavenger underflow concentrate; and (cc) discarding the phosphatepoor scavenger overflow tailing.

In the process of this invention, a pebble phosphate ore matrix is mined with conventional mining apparatus (e.g., draglines, bulldozers, mechanically driven scoops, buckets, shovels, and the like). The thus mined matrix is converted to a pulp by adding water and agitating, preferably by adding water under high pressure from hydraulic guns, hydraulic cannons, hydraulic jets, or the like; however, other well known types of agitating means (e.g., mechanically driven impellers or propellers, or the injection of steam or air, under pressure, into a matrixwater mixture) can be used, but such methods are generally more expensive and less efiicient than hydraulic guns, jets, or the like. The matrix can be converted to a pulp in the field (i.e., at or near the ore deposit from which the matrix was mined) and then pumped to a washing zone (a so-called washing plant). If the pulp is prepared at an elevation higher than that of the washing zone, or washing plant, the pulp can flow by gravity to said plant. Alternatively, the mined matrix can be transported (e.g., via truck, railway, ship, or the like) to a position, or location, near the washing plant where said matrix is pulped and pumped or permitted to flow to the washing plant.

Mud balls (i.e., admixtures of clay and sand or admixtures of clay, sand, and phosphate rock particles) present in the pulp are decomposed by washing in at least one log washer, by passing the pulp through a trough while directing a plurality of jets of water under high presure (e.g., ca. 200-2,000 pounds per square inch gauge) at the pulp, or by using the method described in U.S. Patent 3,288,283.

The pulp which has been substantially freed of mud balls by disintegrating said mud balls (without grinding the pulp) is deslimed. Washing and desliming (i.e., removing particles smaller than about mesh U.S. Standard) phosphate ore pulp can be accomplished by passing the pulp into hydroseparators and permitting the slime to overflow, by using cone classifiers, washing boxes, mechanical classifiers, or the like.

The deslimed pulp is screened while wet. This can be done with conventional wet screening apparatus such as woven wire screens, wedge wire screens, bar screens, and the like, to produce a first sized fraction of said pulp, said first sized fraction having a particle size distribution of about:

U.S. Standard mesh: Weight percent The figures in the table immediately above mean that substantially all of the solid particles comprising the aforesaid first size friction will pass a 5 mesh U.S. Standard screen. Said figures also means that if a 500 gram (dry weight) sample of the solid ore particles comprising the aforesaid first sized fraction is subjected to a conventional screen analysis using a sequence of screens consisting of 5, 6, 14, 20, 28, 35, 65, and 150 mesh U.S. Standard screens over a receiving pan, said screens being arranged in a stack, or sequence, based on the order of their mesh size with the coarsest (largest mesh) screen (i.e., the mesh US. Standard screen) placed at the top of the stack and with the finest (smallest mesh) screen (i.e., the 150 mesh US. Standard screen) placed at the bottom of the stack of screens immediately over a receiving pan, the dry weight of particles retained on each screen and in the receiving pan is about:

Screen size, Weight in grams of and that the total dry weight of the particles retained on the screens plus the weight of particles passing the 150 mesh screen and collected in the receiving pan positioned at the bottom of the stack of screen is 500 grams (where screening a sample weight 500 grams (dry weight)).

A first feed pulp is prepared by adjusting the moisture content of the first sized fraction to about 20-30% (pref: erably about 24-26%) by weight by adding water to said first sized fraction or by dewatering said fraction. A pebble phosphate ore pulp can be dewatered by using cone dewaterers, spiral classifiers, mechanical classifiers including rake classifiers, and the like.

The pH of the first feed pulp is adjusted to about 8.5- 11 (preferably about 8.5-9.5) by adding alkali (e.g., NaOH or KOH) preferably in the form of a solution. The pulp, after its pH has been adjusted is subjected to froth flotation in at least one froth flotation cell (rougher cell) in the presence of an anionic flotation reagent of the type discussed infra, thereby to produce a phosphate-rich rougher overflow concentrate and a phosphate-poor rougher underflow tailing. Said concentrate and said tailing are recovered separately for further concentration by one of two general procedures. The first general procedure is described in more detail in Examples 11 and IV, infra, and the second general procedure is described in more detail in Example V, infra. The above-described steps, i.e., mining, pulping, desliming, screening, and flotation in at least one rougher froth flotation cell with an anionic flotation reagent are also set forth in Examples I-V, infra.

The processing apparatus (including flotation cells) used in the process of this invention does not constitute a part of the invention because each step of the invention can be conducted in conventional apparatus. The invention lies in the beneficiation of an unground pebble phosphate ore matrix by a procedure, or method, comprising the sequence of steps set forth in the claims.

Anionic flotation (i.e., froth flotation in the presence of an anionic flotation reagent) is effective to remove, as overflow, a substantial amount of the phosphate values together with a small portion of sand (silica gangue, silica, silicates, and the like). Most of the sand and gangue together with a smaller portion of the phosphate values pass into the underflow as tailing. Cationic flotation is effective to remove, as underflow, a substantial amount of the phosphate values together with a small portion of sand. Most of the sand, and a smaller portion of the phosphate values, pass into the overflow as tailing.

The particular anionic flotation reagents utilized in the rougher flotation of the phosphate ore do not constitute an essential feature of this invention which is operable with and contemplates all such reagents. Representative conventional anionic reagents comprise the fatty acids, fatty acid soaps, particularly mixed fatty acids or soaps thereof, fatty acids derived from natural sources such as tall oil soaps and the like, fatty acids or soaps of acids derived from animal or vegetable fats, esters of inorganic acids with high molecular alcohols, and the like. Conventionaly such anionic reagents are applied in solution or in a dispersion in a carrier medium such as hydrocarbon oil (e.g., fuel oil or kerosene). One widely used specific reagent comprises about 1-3 parts by volume of tall oil to about l-4 parts by volume of fuel oil; if desired, up to about 4 parts by volume of kerosene can be added to this mixture.

Neither do the particular cationic flotation reagents untilized in the process of this invention constitute an essential feature of my invention which is operable with and contemplates all such reagents. Such reagents include, but are not limited to, higher aliphatic amines (e.g., 014-013 amines) and their salts with water-soluble acids, the esters of amino alcohols with high molecular weight fatty acids and their salts with watersoluble acids, the higher alkyl-O-substituted isoureas and their salts with water-soluble acids, the higher aliphatic quaternary ammonium bases and their salts with watersoluble acids, the higher alkyl pyridinium salts of watersoluble acids, and the higher alkyl quinolinium salts of water-soluble acids, and the like.

It has been found that the pH of pulps can be raised by adding caustic (e.g., caustic soda or caustic potashpreferably in the form of solutions) to said pulps. It has also found that the pH of pulps can be lowered by adding acid (e.g., H HCl, and the like) to said pulps. Said acid can be added in concentrated form or as a dilute aqueous solution.

As stated supra, in the process of this invention pulps can be washed and deslimed with such apparatus cyclone separators (from which the slimeparticles passing about a mesh, US. Standard screen-and wash water and oil and oil soluble reagents overflow), overflow washersincluding overflow box washers-counterflow hydro-deslimers, and the like.

It is understood that this invention is not limited to the following specific examples, which are offered merely as illustrations; it is also understood that modifications can be made without departing from the spirit of this invention.

Example I A phosphate martix was mined from a deposit of pebble phosphate ore using a. dragline, the thus mined matrix was pulped at the mine site with a jet of water from a hydraulic gun to produce a pulp having a solid content of about 30-35%. Said pulp was pumped to a washing plant where it was freed of mud balls by washing in log washers and deslimed (freed of particles passing about a 150 mesh, US. Standard screen) by passing through cyclone separators. The overflow (containing the slime) was discarded and the underflow having a solid content of about 50-60% was recovered and diluted with water to a solid content of about 25-30%. The thus diluted pulp was passed to a rake classifier where it was separated into two fractions; (a) fraction A which was very rich in particles passing a 35 mesh US. Standard screen; and (b) fraction B which was relatively poor in particles passing a 35 mesh U.S. Standard screen.

Example ll 9 44% home phosphate of lime (BPL) and had a screen analysis of about:

US. Standard mesh: Weight percent 1 Trace 1 Less than 0.1%.

Water was added to the first sized fraction at such rate as to reduce the solid content thereof to about 25%. Caustic soda solution was added to adjust the pH to about 8.5, and an anionic flotation reagent was added to the thus prepared pulp at the rate of about 5.3 lbs. of reagent per ton of solid content. Said reagent was prepared .by mixing tall oil (2 parts by volume), fuel oil (1 part by volume), and 0.6 part by volume of a 20% solution of caustic soda. The resulting reagent-treated pulp was subjected to froth flotation in rougher cells to yield an overflow (rougher concentrate) of about 76 tons of solid, dry basis, per hour analyzing 63% BPL and an underflow (rougher tailing) of about 42 tons of solid, dry basis, per hour analyzing 9% BPI.

The rougher tailing passed to a sump from which it was pumped through a cyclone separator which deslimed the rougher tailing. The cyclone overflow was sent to waste, and the underflow was discharged into a spiral classifier to dewater the pulp to a solid content of about 70%. After adding fresh (deep well) water to adjust the solid content of the dewatered discharge from the spirals to about 25%, the resulting pulp had a pH of about 6.8-7. Thus, it was not necessary to adjust the pH of said pulp. Said pulp was passed into the feed end of a row of scavenger cells where cationic flotation reagent (an aqueous dispersion of 3.3% C -C aliphatic amines and 1.7% rosin) was added to said pulp at the rate of about 0.39 lb. of amine per ton of pulp. The resulting mixture was subjected to flotation in a row of scavenger cells, whereby a sand scavenger tailing overflow (ca. 37 tons, dry basis, of solid per hour analyzing 1.1% BPL) and a phosphate-rich scavenger underflow concentrate (ca. tons, dry basis, of solid per hour analyzing 66% BPL) were produced. The sand tailing was discarded. The aforesaid phosphate-rich scavenger underflow was collected and added to the rougher concentrate.

The resulting mixture of rougher concentrate and phosphate-rich underflow from the cationic flotation of the rougher tailing was treated with sulfuric acid (2.5 lbs. H 50 per ton of pulp) and partially dewatered and partially deoiled (i.e., partially freed of anionic flotation reagent) by passing through a deoiling cyclone separator. The overflow from the cyclone was discarded and the cyclone underflow Was washed with water in washing boxes (to further deoil said underflow) and dewatered in a screw classifier. The pulp discharged from said classifier was substatnially free of both H 80 and anionic flotation reagents. Said pulp had a solid content of about 70%; after its solid content was adjusted to about 25%, by adding water, the thus diluted pulp had a pH of about 6.9-7.2. Said pulp was subjected to flotation in a row of cleaner cells using a cationic flotation reagent (an aqueous dispersion of 3.3% C14-C18 aliphatic amines and 1.7% rosin) which was added to the pulp at the rate of about 0.22 lb. of amine per ton of pulp. This treatment resulted in the production of a sand tailing as cleaner overflow (ca. 13 tons of solid, dry basis, per hour analyzing 12% BPL) and a phosphate-rich cleaner underflow concentrate (ca. 68 tons of solid, dry basis, per hour analyzing 73% 10 BPL). The phosphate-rich underflow concentrate as recovered, and the sand tailing was discarded.

Example 111 The general procedure of Example I was repeated. However, in this instance the pebble phosphate ore was mined from a deposit of slightly lower grade than that in Example I. A fraction of pulp relatively poor in particles passing a 35 mesh US. Standard screen was collected and designated Pulp B.

Example IV Pulp B was screened using the general procedure of Example II to produce a first sized fraction at the rate of about 109 tons (solid content) per hour, the solid content of said fraction analyzing about 35% BPL and having a screen analysis of about:

US. Standard mesh: Weight percent 5 +6 0.4 +14 37.1 +20 20.6 +28 16.6 +35 14.6 +48 7.6 +65 2.2 0.8 150 0.1

Water was added to the first sized fraction at such rate as to reduce the solid content thereof to about 26%. Caustic soda solution was added to adjust the pH to about 8.5-8.7 and an anionic flotation reagent was added to the thus prepared pulp at the rate of about 4 lbs. of reagent per ton of solid content. Said reagent was prepared by mixing tall oil (2 parts by volume), fuel oil (1 part by volume), and 0.6 part by volume of a 20% solution of caustic soda. The resulting reagent-treated pulp was subjected to a rougher flotation to yield an overflow (rougher concentrate) of about 55 tons of solid, dry basis, per hour analyzing 54% BPL and an underflow (rougher tailing) of about 54 tons of solid, dry basis, per hour analyzing 16% BPL.

The rougher tailing passed to a sump from which it was pumped through a desliming cyclone separator which also partially dewatered the pulp (rougher tailing). The cyclone overflow as sent to waste, and the underflow was discharged into a spiral classifier to dewater the pulp. After adding fresh (deep well) water to adjust the solid content of the dewatered discharge from the spirals to about 26%, the resulting pulp had a pH of about 6.9-7. Said pulp was passed into the feed end of a row of scavenger flotation cells where cationic flotation reagent (a 5% dispersion of C -C aliphatic amine in water) was a-dded to the pulp thus prepared from the rougher tailing at the rate of about 0.17 lb. of amine per ton of pulp. The resulting mixture was subjected to flotation in the scavenger cells, whereby a sand tailing scavenger overflow (ca. 42 tons, dry basis, of solid per hour analyzing 3% BPL) and a phosphate-rich scavenger underflow concentrate (ca. 12 tons, dry basis, of solid per hour analyzing 61% BPL) was produced. The sand tailing was discarded. The aforesaid phosphate-rich scavenger underflow concentrate was collected and added to the rougher concentrate.

The resulting mixture of rougher concentrate and phosphate-rich underflow from the cationic flotation of the rougher tailing was treated with sulfuric acid (2.5 lbs. H 80 per ton of pulp) and partially dewatered and partially deoiled (i.e., partially freed on anionic flotation reagent) by passing through a deoiling cyclone separator. The overflow from the cyclone was discarded and the cyclone underflow was washed with water in washing boxes to further deoil said underflow. The thus deoiled cyclone underflow was dewatered in a screw classifier.

The pulp discharged from said classifier had a solid content of about 71%, said pulp was substantially free of both H 80 and anionic flotation reagents. Said pulp was adjusted to a solid content of about 24%; its pH was about 7.0-7.2. Said pulp was subjected to froth flotation in a row of cleaner cells using a cationic flotation reagent (a dispersion of C -C aliphatic amines in water) which was added to the pulp at the rate of about 0.18 lb. of amine per ton of pulp. This treatment resulted in the production of a sand tailing as overflow, ca. 15 tons of solid, dry basis, per hour analyzing 9% BPL and a phosphate-rich product, as underflow, ca. 52 tons of solid, dry basis, per hour analyzing 70% BPL. The phosphaterich product was recovered as final product, and the sand tailing was discarded.

Example V Fraction B (from Example I) was screened using the general procedure of Example II to produce a first sized fraction at the rate of about 115 tons per hour (solid content), the solid content of said fraction analyzing about 44% BPL and having a screen analysis of about:

US. Standard mesh: Weight percent Less than 0.1%.

Water was added to the first size fraction at such rate as to form a pulp having a solid content thereof to about 26%, caustic soda solution (ca. 20% NaOH) was added to adjust the-pH of the pulp to about 9, and an anionic flotation reagent was added to the thus prepared pulp at the rate of about 2.5 lbs. of reagent per ton of solid content. Said reagent was prepared by mixing tall oil (2 parts by volume), fuel oil (1 part by volume), and 0.6 part by volume of a 20% solution of caustic soda. The resulting reagent-treated pulp was subjected to a rougher froth flotation to yield an overflow (rougher concentrate) of about 65 tons of solid, dry basis, per hour analyzing 66% BPL and an underflow (rougher tailing) of about 50 tons of solid, dry basis, per hour analyzing 14% BPL.

The rougher concentrate was treated with sulfuric acid (2.5 lbs. H 50 per ton of pulp), said concentrate was partially deoiled (i.e., partially freed of anionic flotation reagent) and partially dewatered by pasing through deoiling cyclone separators. The overflow from the cyclones was discarded and cyclone underflow was washed with water in washing boxes (to further deslime and deoil said underflow). The washing cyclone underflow was dewatered in a screw classifier. The pulp discharged from said classifier was substantially free of both H 50 and anionic flotation reagents. Said pulp, after its solid content was adjusted to about 25%, had a pH of about 6.8-7. Said pulp was subjected to froth flotation (a cleaner flotation) using a cationic flotation reagent (a 5% dispersion of C14C13 aliphatic amines in water) which was added to the pulp at the rate of about 0.2 lb. of amine per ton of pulp. This treatment resulted in the production of a sand tailing as overflow, ca. 9 tons of solid, dry basis, per hour analyzing 11% BPL and a phosphate-rich, product, as underflow, ca. 56 tons of solid, dry basis, per hour analyzing 11% BPL and a phosphate-rich product, as underflow, ca. 56 tons of solid dry basis, per hour analyzing 76% BPL. The phosphaterich cleaner underflow was recovered as a final product, and the phosphate-poor cleaner tailing was recovered separately for further concentration.

The phosphate-poor rougher underflow tailing and the phosphate-poor cleaner overflow tailing were combined and treated with sulfuric acid (ca. 2.5 lbs. of H SO per ton of pulp), partially washed, and partially deoiled by being passed through cyclone separators. The overflow from the cyclones was discarded and the underflow was washed with fresh well water in washing boxes, to further deoil the pulp. (Treatment in the cyclone separators and in the washing boxes also deslimed the pulp.) The washed pulp was dewatered to a solid content of about 57% in a screw classifier, and water was added to adjust the solid content of the thus dewatered pulp to about 25%. The pulp was substantially free of H and anionic flotation reagents; its pH was about 6.9-7. Said pulp, having a pH of about 6.9-7, was subjected to a froth flotation in scavenger cells using a cationic flotation reagent (a 5% dispersion of C14-C18 aliphatic amines in water) which was added to the pulp at the rate of about 0.25 lb. of amine per ton of pulp. The phosphate-rich scavenger underflow concentrate was recovered and the phosphatepoor scavenger overflow tailing was discarded.

As used herein the term percent unless otherwise defined or qualified where used, means percent by weight; the term lb. means pound; and the term lbs. means pounds.

I have found that washing and diluting pulps comprising concentrates, or tailings, or mixed concentrates and tailings from previous flotation steps usually adjusts the pH of the thus washed pulps to about 6.8-7.3, thereby eliminating the necessity of further adjusting the pH of the thus washed pulps. However, where necessary or desirable, the pH of such pulp can be lowered by adding acid or increased by adding alkali.

The process of this invention is limited to the use of unground pebble phosphate ore in all of the froth flotation steps recited herein. Neither ore nor pulps are ground in any step of this process, except for such attrition as occurs in circulating pulps in the process of this invention. Specifically, no grinding apparatus such as crushers, mills, and the like is used in the process of this invention.

What is claimed is:

1. A method for beneficiating unground pebble phosphate ore comprising:

(a) mining a pebble phosphate ore matrix;

(b) preparing an aqueous unground pulp of said matrix;

(c) flowing said aqueous pulp to a washing plant;

(d) disintegrating mud balls present in said aqueous pulp without grinding said pulp;

(e) desliming the washed aqueous pulp;

(f) wet screening the deslimed unground aqueous pulp and collecting a first sized fraction of the unground aqueous pulp, the solid particles of said first sized fraction having a particle size distribution of about:

U.S. Standard mesh: Weight percent phosphate-rich rougher overflow concentrate and a phosphate-poor rougher underflow tailing;

(j) recovering the phosphate-rich rougher overflow concentrate for further concentration in later recited steps;

(k) separately recovering the phosphate-poor rougher underflow tailing for further concentrating in later recited steps;

(1) desliming the phosphate-poor rougher underflow tailing by washing said tailing with water;

(111) preparing a first thick pulp by dewatering the washed and deslimed phosphate-poor rougher underflow to a solid content of about 65-75%;

(n) preparing a second feed pulp by adding fresh water to adjust the solid content of the first thick pulp to about 20-30%;

(o) preparing a scavenger feed pulp by adjusting the pH of the second feed pulp to about 6.8-7.3;

(p) subjecting the scavenger feed pulp to froth flotation in at least one scavenger flotation cell in the presence of a cationic flotation reagent to produce a phosphate-rich scavenger underflow concentrate and a phosphate-poor scavenger overflow tail- (q) recovering the phosphate-rich scavenger underflow concentrate for further concentration in later recited steps;

(r) discarding the phosphate-poor scavenger overflow tailing;

2. A method for beneficiating unground pebble phosphate ore comprising:

US. Standard mesh: Weight percent +5 100 +6 -2 +14 -40 +20 +25 +28 s 20 +35 7-18 +65 1 s0 +150 0.s 30 150 0-5 (g) preparing a first feed pulp from the first sized fraction of unground aqueous pulp by adjusting the solid content of said first sized fraction to about 20-30%;

(h) preparing a rougher feed from said first feed pulp by adjusting the pH of said first feed pulp to about 8.5-11;

(i) subjecting said rougher feed to froth flotation in at least one first rougher flotation cell in the presence of an anionic flotation reagent to produce a phosphate-rich overflow concentrate and a phosphatepoor rougher underflow tailing;

(j) recovering the phosphate-rich rougher overflow concentrate for further concentration in later recited steps;

(k) separately recovering the phosphate-poor rougher underflow tailing for further concentrating in later recited steps;

(1) treating the phosphate-rich rougher overflow concentrate with mineral acid;

(in) partially dewatering and partially deoiling the acid-treated phosphate-rich rougher overflow concentrate;

(n) deoiling the acid-treated partially dewatered and partially deoiled phosphate-rich rougher overflow concentrate by washing said concentrate with fresh Water;

(0) preparing a first thick pulp by further dewatering the deoiled phosphate-rich rougher underflow concentrate to a solid content of about 65-75%;

(p) preparing a second feed pulp by adding fresh water to adjust the water content of the first thick pulp to about 20-30%;

(q) preparing a cleaner feed pulp by adjusting the pH of the second feed pulp to about 6.8-7.3;

(r) subjecting the cleaner feed pulp to froth flotation in at least one cleaner flotation cell in the presence of a cationic flotation reagent to produce a phosphaterich cleaner underflow concentrate and a phosphatepoor cleaner overflow tailing;

(s) recovering the phosphate-rich cleaner underflow concentrate;

(t) separately recovering the phosphate-poor cleaner overflow tailing for further concentration in later recited steps;

(u) forming a mixed pulp by combining the phosphatepoor rougher underflow tailing and the phosphatepoor cleaner overflow tailing;

(v) treating the mixed pulp with mineral acid;

(w) partially dewatering and partially deoiling the acid-treated mixed pulp;

(x) deoiling the acid-treated partially dewatered and partially deoiled mixed pulp by washing said pulp with fresh water;

(y) forming a second thick pulp by desliming and dewatering the deoiled mixed pulp to a solid content of about 50-60%;

(2) forming a third feed pulp by adding fresh Water to adjust the solid content of the second thick pulp to about 20-30%;

(aa) forming a scavenger feed pulp by adjusting the pH of the third feed pulp to about 6.8-7.3;

(bb) subjecting the scavenger feed to froth flotation in at least one scavenger flotation cell in the presence of a cationic flotation reagent to produce a phosphate-rich scavenger underflow concentrate and a phosphate-poor scavenger overflow tailing;

(cc) recovering the phosphate-rich scavenger underflow concentrate; and

(dd) discarding the phosphate-poor scavenger overflow tailing.

3. The process of claim 1 in which the solid content of the rougher feed pulp is about 24-26% and the pH of said pulp is about 8.5-9.5.

4. The process of claim 1 in which the solid content of the scavenger feed pulp is about 24-26% and the pH of said pulp is about 6.8-7.3.

5. The process of claim 1 in which the solid content of the cleaner feed pulp is about 24-26% and the pH of said pulp is about 6.8-7.3.

6. The process of claim 1 in which the solid content of the second thick pulp is about 69-71%.

7. The process of claim 2 in which the solid content of the rougher feed pulp is about 24-26% and the pH of said pulp is about 8.5-9.5.

8. The process of claim 2 in which the solid content of the scavenger feed pulp is about 24-26% and the pH of said pulp is about 6.8-7.3.

9. The process of claim 2 in which the solid content of the cleaner feed pulp is about 24-26% and the pH of said pulp is about 6.8-7.3.

10. The process of claim 2 in which the solid content of the second thick pulp is about 55-58% (References on following page) References Cited UNITED STATES PATENTS Crago 209166 Lawver 209166 Hunter 209-466 Le Baron 209-166 1 6 3,008,575 11/1961 ClaWson 209-12 3,009,620 7/1963 Adam 209-12 HARRY B. THORNTON, Primary Examiner. 5 R. HALPER, Assistant Examiner. 

1. A METHOD FOR BENEFICIATING UNGROUND PEBBLE PHOSPHATE ORE COMPRISING: 